In the coal industry, various types of shale and clay are produced as a mixture with the coal, to increase the heating value of the coal and to reduce the hauling costs, a complex process of coal washing is normally used to reduce the total ash content. In this process the coal is graded to a certain size, usually less than 15 mm and greater man ½ mm and then fed into a dense medium cyclone.
The usual practice for separation of fine particles (less than ½ mm) of coal contained in coal slurry through the use of froth flotation processes is well known. Froth flotation processes involve introducing air into the coal slurry. The hydrophobic particles of coal are contacted with finely disseminated air bubbles such that the fine air bubbles become adhered to the hydrophobic coal particles.
The particles carrying bubbles are then permitted to rise, forming froth on the surface of the slurry. The froth, containing the hydrophobic particles of coal, is skimmed from the surface of the coal slurry and collected, while rejecting any hydrophilic particles of impurities which don't adhere to the air bubbles and which remain suspended in the slurry.
Flotation of coal fines has become increasingly important as a separation and cleaning process where there is lowering in both the particle size and grade of the coal being recovered from mining operation. The ability to remove the coal fines from coal washery or tailings is also advantageous in order to recover coal fines missed by other techniques of coal recovery.
In order to improve the selectivity and recovery of the flotation process and enhance floating of the coal fines, various types of reagent have been developed for addition to the slurry. Frothers and collectors are two types of reagents which are commonly used in coal flotation. A frothing agent is utilized to provide stable flotation froth persistent enough to facilitate the coal separation but not so persistent that it cannot be broken to allow subsequent handling.
The use of froth flotation to effect a separation of ash particles from coal can be achieved only if liberation of these unwanted particles form the coal has taken place, Most high-grade coals are flotable naturally due to their hydrophobic surface and typically only require a frothing agent for effecting flotation. A frothing agent imparts elasticity to the air bubbles, enhances particle-attachment so that the coal is buoyed to the surface of the slurry.
Conventional frothers can be essentially divided into four groups. The first group consists of aromatic alcohols such as α-eresol and 2,3-xylenol. A second group is the alkoxy types such as triethoxy butane (TEB). The third group consists of aliphatic alcohol such as 2-ethyl hexanol, diacetone and methyl isobutyl carbinol (MIBC). In recent years, a fourth group of synthetic frothers consisting of PEO (polyethylene oxide), PPO (polypropylene oxide) and PBO (polybutylene oxide) types have been introduced into the market. These chemicals may be presented by the general equation; R (X)nOH where R=H or CnH2n+1 and X=EO, PO or BO.
General problems associated with the conventional frothing agents and recent developed frother are I) Not effective for both coarse and ultrafine particles for wide size distributed flotation feed (0.5×0.0 mm). It is due to some frothers are effected for coarse particles and others are good for floating ultra fine fractions, II) Incapability of producing low ash content clean coal form highly ash mineral particle disseminated and difficult to float type of coal like Indian coal. Examples of patents directed at improved frothers include U.S. Pat. No. 4,582,596 issued Apr. 15, 1986, U.S. Pat. No. 4,915,825 issued Apr. 10, 1990. U.S. Pat. No. 4,272,364 issued Jun. 9, 1981, U.S. Pat. No. 4,504,385 issued Mar. 12, 1985, U.S. Pat. No. 5,304,317 issued Apr. 19, 1994, U.S. Pat. No. 3,710,939 issued Jan. 16, 1973, U.S. Pat. No. 4,606,818 issued Aug. 19, 1986, U.S. Pat. No. 4,761,223 issued Aug. 2, 1988, U.S. Pat. No. 4,925,559 issued May 15, 1990. Therefore, the present inventors have developed a frother which comprises ketone and ester functional group with a small quantity of conditioning agent. This novel frother overcomes the many disadvantages of the aforementioned conventional and earlier invented frothers, as well as provide the following advantages: increased clean coal recovery with better selectivity, a frother having both frother and collector properties when used in coal flotation processes.